1. Field of the Invention
The present invention relates to microstructures, such as microelectromechanical systems (MEMS), manufactured from wafers by semiconductor manufacturing processes; microstructure arrays each including a plurality of the same; and methods of manufacturing the same, and in particular to a technique of forming, on a substrate, a structure including a movable portion. Basically, microstructures are of microscopic sizes in, for example, micrometer order, and include movable portions. Microstructures are applicable to dynamic quantity sensors (acceleration sensors, pressure sensors, gyroscopic sensors, and the like), optical deflectors, optical switches, optical modulators, and the like.
2. Description of the Related Art
Hitherto, microelectromechanical systems (MEMS) have been in use as actuators, sensors, and the like (as disclosed in U.S. Patent Application Publication No. 2009/0067033 A1 and Japanese Patent Laid-Open No. 2007-248731). For example, a movable portion is provided on a substrate, and the substrate and the movable portion in combination form a variable capacitor in which the capacitance is variable. Such a capacitor can function as an electrostatic actuator or a sensor that detects any change of capacitance. In another case, a device in which a microstructure is provided on a substrate having an integrated circuit. A microstructure in such a device is utilized as, for example, an optical deflector that deflects light. In yet another case, a plurality of microstructures are provided in the form of an array. In particular, a MEMS device that two-dimensionally deflects light with a plurality of microstructures each including a movable portion having a reflective surface can function as an optical switch, a spatial intensity modulator, a phase modulator, or the like.
In general, a microstructure including a movable portion provided on a substrate has low rigidity and is easy to undergo unintentional deformation. Unintentional deformation is caused by stresses produced in manufacturing individual elements, internal stresses acting inside the elements due to change of temperature, an inertial force under the movable portion's own weight occurring when the movable portion is displaced, external forces, or the like. Particularly, there has been a problem in that it is not easy to prevent unintentional deformation while reducing the spring constant of an elastic supporting portion, in the direction of designed displacement, that supports the movable portion allowing the movement of the movable portion.